Anyone who works any kind of assembly line job can't just leave for a few minutes without causing problems. Bio breaks are usually taken at scheduled breaks.
(based on my summer jobs at the mill, at least)
I worked a couple entry-level (i.e., menial minimum wage shit) jobs and I never had to ask permission (even when I was a cashier during lunch hour at a popular local fast food restaurant) so I have no idea where that came from.